Is 87 octane bad for 70's and older cars?

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Mikej89

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Apr 1, 2014
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I ran into an older gentleman that was admiring my 1978 Cadillac. He asked me what gas I run in it and I told him 87 regular. He then told me that 87 octane pump gas has alcohol in it which is bad for the fuel system on older cars. He advised me to run 89 octane instead.

So...... I'm always skeptical when I hear something from just one person, of course. But he knew a lot about old Cadillacs and is a collector himself. What's the consensus here? I really don't want to burn more expensive gas if I don't need to, but I certainly will if neglecting to do so will ruin my fuel system :rolleyes:.
 

MrSony

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Nov 15, 2014
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I think compression was 8.2:1, or lower. 87 is perfectly fine, it's the alcohol that has him worried. I think all 87 has alcohol in it, while some stations sell 89 as straight gasoline.
 

Mikej89

Apprentice
Apr 1, 2014
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I think compression was 8.2:1, or lower. 87 is perfectly fine, it's the alcohol that has him worried. I think all 87 has alcohol in it, while some stations sell 89 as straight gasoline.

But is the alcohol bad for older motors? That's what I was asking. I know the compression ratio is fine for the low octane...
 

MrSony

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Nov 15, 2014
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But is the alcohol bad for older motors? That's what I was asking. I know the compression ratio is fine for the low octane...
Oh, yeah. totally. It eats the rubber lines, draws moisture, boils at a lower temperature. It's terrible for older cars. New cars are designed to run this... swill that we dare call gasoline. Straight gasoline would be better long term. But don't sweat it if you use alcohol gas. Just be careful.
 
Oct 14, 2008
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Only premium here, 91 octane is alcohol free. If your car sits a lot, a good additive might help, Starbrite is supposed to be good. I have decided 91 is the way to go for my 70S and maybe for the 88 as well.
 
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UNGN

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Sep 6, 2016
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Octane number has no bearing on Alcohol content. Because its subsidized by tax dollars, Alcohol is a cheap way to increase octane, so higher octane gas can have more alcohol than lower octane gas.

Running alcohol free gas in an old car is good idea. Running leaded race gas through a car once in a while seems to protect it from the ravages of alcohol gas. My '89 Turbo trans am's fuel tank was solid rust inside, while my '86 T-type's tank was like new inside. The only difference I can think of is when I was racing it, I ran a few gallons of leaded gas in the T-type.
 

Bonnewagon

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Sep 18, 2009
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Any '78 motor is low compression and will run on cat piss. If the alcohol was going to affect the car it would have done so in the first year of use. It flushes out rusty gas tanks, ruins old rubber fuel lines, and swells non-alcohol rated parts like floats and gaskets, and seals. I do notice that my carb bowl evaporates dry in only two or three days so I have modified my starting procedure. I do several short cranks until fresh gas gets to the carb. If you have been using it for a long time with no problems- don't worry about it.
 
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DRIVEN

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Apr 25, 2009
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I'm fortunate that the area I just moved to has better availability of ethanol free gas. All my motorcycles and old cars are now on a steady diet. I can even get alcohol free 87!
 
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